Buying the WRT54G Wireless Router in India

To make my home wi-fi enabled, I decided to buy a Wireless Router. Loads of such routers are available these days and after doing a bit of research online I decided to go for the Linksys WRT54G router.

WRT54G routers allow you to install certain open-source (linux) firmware. If you are the kind who likes to play around with hardware, then this is the one for you. It allows you to do all sorts of things like increase the range (using the Xmit power), port-forwarding etc. etc. For details please goto http://www.dd-wrt.com/.

A friend of mine suggested to go for WRT54G Version-5 or 6 since he already had one and it was working fine with Linux firmware. So... I went to Nehru Place (supposedly THE place to buy computer hardware in New Delhi) and asked for Linksys WRT54G router. Surprisingly the version information wasn't mentioned on the router's box.. I tried a few more shops.... but again, no version information. Hoping that the router will work with linux firmware I decided to purchase the router for Rs. 2150/-. Once I got home and opened the box 'version 7' was mentioned at the back of the router. After a bit of googling it was clear that this version of WRT54G CANNOT be upgraded to Linux firmware. Even if I try to install the firmware, the router will get 'bricked' (basically of no use and will have to be thrown).

If you are planning to buy the WRT54G router and install Linux firmware on it, please ensure that it's NOT 'version 7'. All versions (v5,6,8) can be upgraded to Linux firmware but not v7. The serial number of all WRT54G v7 routers starts with 'CDFE'. The serial number is mentioned on the router's box (wish I knew this early on).

Luckily I found someone who already had a 2 year old v5 WRT54G and was happy to exchange his router with my new v7 router :)

I have now successfully upgraded the v5 router to Linux firmware(dd-wrt) and its working fine.

Hosting multiple sites on a single server using the same IP

Apache has a great feature which allows hosting multiple sites using the same apache instance and even the same IP address. To know more click here

Following example shows how this can be done.

Open the httpd.conf configuration file which is being used by apache.

Add following at the end:

NameVirtualHost 127.0.0.1:80

<VirtualHost 127.0.0.1:80>
ServerAdmin your@email.com
DocumentRoot /doc/root/for/first/domain/
ServerName www.firstdomain.com
ServerAlias www.firstdomain.com
ErrorLog logs/firstdomain_error_log
CustomLog logs/firstdomain_access_log common
</VirtualHost>

<VirtualHost 127.0.0.1:80>
ServerAdmin your@email.com
DocumentRoot /doc/root/for/second/domain/
ServerName www.seconddomain.com
ServerAlias www.seconddomain.com
ErrorLog logs/seconddomain_error_log
CustomLog logs/seconddomain_access_log common
</VirtualHost>

Replace 127.0.0.1 with the appropriate IP address, firstdomain and seconddomain as per the requirement.

Restart apache.

I tried this with apache 2.0.59 and it works fine.

Finding Intersections between two sets in C++

Following C++ code (intersection.cpp) creates 2 sets ( a and b), creates a vector out of those (av and bv) and then finds the intersection between the two vectors.

#include <iostream>
#include <vector>
#include <set>
#include<sys/time.h>

using namespace std;

#define MAX_SIZE 1000000

int main()
{
        set<int> a,b,un,in,di;
        timeval tim;

        srand ( time(NULL) );

        cout << "Adding to a : " << endl;

        for( int i = 0; i < MAX_SIZE; i++ ) {
                int r = rand() % MAX_SIZE;
                a.insert( r );
        }  

        cout << "Creating vector av" << endl;
        vector<int> av(a.begin(),a.end());
        cout << "There are " << av.size() << " elements in av" << endl;

        cout << "Adding to b : " << endl;

        for( int i = 0; i < MAX_SIZE; i++ ) {
                int r = rand() % MAX_SIZE;
                b.insert( r );
        }  

        cout << "Creating vector bv" << endl;

        vector<int> bv(b.begin(),b.end());
        cout << "There are " << bv.size() << " elements in bv" << endl;

        gettimeofday(&tim, NULL);
        double t1=tim.tv_sec+(tim.tv_usec/1000000.0);

        set_intersection(a.begin(),a.end(),b.begin(),b.end(),insert_iterator<set<int> >(in,in.begin()));

        gettimeofday(&tim, NULL);
        double t2=tim.tv_sec+(tim.tv_usec/1000000.0);

        vector<int> inv(in.begin(),in.end());

        cout << "Elements in intersection " << inv.size() << endl;
        cout << "Intersection time " << (t2-t1) << " seconds" << endl;
        return 0;
}

compile: c++ intersection.cpp -o intersection
Sample Output

./intersection
Adding to a :
Creating vector av
There are 632163 elements in av
Adding to b :
Creating vector bv
There are 631924 elements in bv
Elements in intersection 399250
Intersection time 0.65199 seconds

Technologies to look out for in 2008

Here are a bunch of exciting technologies to look out for this year:

1) Wireless USB: Tired of carrying all those wires with your USB devices. Well... there is hope of getting rid of them. Wireless USB is capable of high speed data transfer (much faster than Bluetooth). http://en.wikipedia.org/wiki/Wireless_USB

2) Solid State Drive (SSD): These are the next generation of Disk Drives. They should be hugely successful with mobile devices (like laptops n phones) coz they are mechanically very reliable. They have the ability to endure extreme shock, high altitude, vibration and temperatures. http://en.wikipedia.org/wiki/Solid_state_disk.

3) Organic Light-Emitting Diode (OLED): Much more efficient than the traditional LED and plasma due to their low power consumption and ability to provide more color depth without any backlight. Extremely thin TVs with amazing colors will be possible with this technology. http://en.wikipedia.org/wiki/Organic_light-emitting_diode.

4) Near Field Communication (NFC): This is a short range, high-frequency wireless communication technology aimed primarily at usage in the mobiles. This makes things like Mobile ticketing and payment possible. http://en.wikipedia.org/wiki/Near_Field_Communication.

Removing all non-ASCII characters from a string using php

ASCII characters have hex code from 00 to 7F (http://www.asciitable.com/).

Following php function removes all non-ASCII characters from a string:

function removeNonAscii($string) {
return preg_replace('/[^\x00-\x7f]/','',$string);
}

Reliance Broadnet (Broadband internet connection)

I recently got a pamphlet of Reliance Broadnet (Broadband service provided by Reliance in India) which mentions that the service provides download speeds ranging from 150 Kbps to 2 Mbps.

Following are the plans mentioned:

1. Rs. 750/month for 150 Kbps (unlimited upload and download)
2. Rs. 999/month for 300 Kbps (unlimited upload and download)
3. Rs. 1799/month for 600 Kbps (unlimited upload and download)
4. Rs. 750/month for speed upto 2 Mbps with free usage of 4 GB (upload+download) and 90 paise/MB for additional usage

Installation charge is Rs. 500 + Service Tax.

Call 1-800-227773 or 3033 7777 for details.

Set Clipboard contents from command line using java

Following code(setClipboardContents.java) sets the Clipboard contents for 10 seconds:


import java.awt.datatransfer.StringSelection;
import java.awt.Toolkit;
import java.awt.datatransfer.Clipboard;

public class setClipboardContents{
public static void main(String[] args) throws Exception {
StringSelection stringSelection = new StringSelection( args[0] );
Clipboard clipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
clipboard.setContents( stringSelection, null);
try{
Thread.sleep(10000);
} catch(InterruptedException e){
System.out.println("Sleep Interrupted");
}
}
}

Compile: javac setClipboardContents.java
Run: java -cp . setClipboardContents "add this content to the Clipboard"

Capturing string input without echo in java

Following code will demonstrate capturing a string without any echo using java:

Create a java file (noEcho.java) with the following code:

import java.lang.System;
import java.io.Console;

public class noEcho {
public static void main(String[] args) throws Exception {
char[] passwd;
Console cons;
if ((cons = System.console()) != null && (passwd = cons.readPassword("[%s]", "Enter Text:")) != null) {
String text = new String(passwd);
System.out.println("You Entered :"+text);
}
}
}

Compile: javac noEcho.java
Run: java -cp . noEcho
Sample output:

[Enter Text:]
You Entered :this is a test string

Hibernate instead of Shutdown for faster performance

When you boot your computer, certain critical modules (like kernel) are loaded into the Primary Memory (RAM) which allow the operating system to start. After this whenever you start an application (like Microsoft Word or Outlook) it first gets loaded into the Primary Memory from where the OS loads the Application. Thus, the first time you start an application there might be a delay of a few seconds and the next time it'll be much faster.

Hibernate saves the contents of the RAM into Secondary Memory (Hard Disk) and when you boot the OS next time, it simply loads the RAM image back from the Hard Disk.

Thus, even though time taken for a normal boot vs time for a boot after hibernate may be similar, you save a lot of time while working on the same set of applications.